Selectively removing or depositing materials on a semiconductor wafer to form integrated circuit structures from wafers is well known in the art of semiconductor processing. Removal of material from a semiconductor wafer is typically accomplished by employing some type of etching process, such as, reactive ion etching or atomic layer etching. Depositing material on a wafer may involve processes such as chemical and physical vapor deposition (CVD/PVD), molecular beam epitaxy (MBE) or atomic layer deposition (ALD). In semiconductor processing, other plasma-based or emitting processes such as implantation are also known and optically monitored. All such processes are tightly controlled and are done in an environmentally controlled process chamber. Because exact amounts of material are to be deposited onto or removed from the surface of a wafer, the deposition or removal progress must be continually and accurately monitored to precisely determine the endpoint or characteristic state of a particular process.
Optically monitoring the chamber process is one very useful tool for determining the processing status, processing state conditions or endpoint for an ongoing process. For instance, the conditions interior to the chamber may be optically monitored for certain known emission lines by analyzing predetermined wavelengths of light emitted or reflected from within the chamber. Conventional optical monitoring methods include optical emission spectroscopy (OES), absorption spectroscopy, reflectometry, interferometric endpoint (IEP), etc.
OES is widely used in the semiconductor industry for monitoring the state of a wafer process within a process chamber by measuring and characterizing the plasma optical emission generated within the process chamber. While OES techniques may vary with the particular application and process, typically the optical emission intensities are monitored at one or more predetermined wavelengths. Monitored processes include semiconductor etching, deposition, implantation and other processes where film thickness and plasma/wafer emission monitoring is applicable. Additionally, chamber conditions independent of or combined with the wafer conditions, may be monitored. Depending on the process, various algorithms may be employed for deriving parameters from the optical signal intensities that are useful in assessing the state of the semiconductor process and the processed wafer, detecting faults associated with the process, chamber or other equipment and even the condition of interior surfaces of the plasma chamber.